Key points:
- Engineering data of Deep SOLO float descent rates serendipitously
reveal vertical velocity signatures of internal waves
- Deep internal wave vertical velocities have typical sinusoidal
amplitudes of 0.007 dbar s-1 and vertical
wavelengths of ~400–1600 dbar
- Vertical velocity variances and dominant vertical wavelengths exhibit
geographical patterns, varying among and within deep ocean basins
Index Terms: 4544 Internal and inertial waves, 4562
Topographic/bathymetric interactions, 4568 Turbulence, diffusion, and
mixing processes, 4223 Descriptive and regional oceanography 4262 Ocean
observing systems
Keywords: Deep Argo; Deep Ocean; Vertical Velocity
Abstract Serendipitous measurements of deep internal wave signatures
are evident in variations in the descent rates of certain Deep Argo
floats (Deep SOLO models), which oscillate around a slow decrease with
increasing pressure (and density). Averaged from 1000 dbar to the
seafloor (using 10070 profiles that extend to at least 3000 dbar, and
sometimes as deep as 6000 dbar) the mean of vertical velocity variances
corresponds to a sinusoidal wave amplitude of about 0.007 dbar
s-1. The distribution of variances is skewed towards
larger values. They also exhibit notable regional variations among and
within some deep ocean basins, with generally larger variances in
regions of rougher topography or stronger deep currents. Dominant
vertical wavelengths estimated from Morlet wavelet transform power
spectra range from 393 to 1572 dbar, most frequently 786 and 935 dbar.
Vertical wavelengths are weakly anticorrelated with bathymetric
roughness, expectedly since shorter wavelengths should be found near
generation regions.
Plain Language Summary Ocean density increases with increasing
depth, supporting internal waves below the ocean surface. These internal
waves are generated near the surface by unsteady wind forcing such as
passing storms and near the bottom by interactions of currents
(including tidal) with rough topography. They can carry energy for long
distances in both the vertical and the horizontal. When they break, they
play important roles in mixing temperature, salinity, and other water
properties. Deep Argo is an observing system designed to measure
temperature and salinity profiles from the surface to the bottom of the
ocean. One model of deep Argo float serendipitously observes internal
wave signals as perturbations in its descent rate, which it records
primarily for navigation purposes, from the surface to the ocean floor.
These observations reveal patterns in the magnitudes of these internal
wave signals, with stronger internal wave activity near rough topography
such as continental rises and mid-ocean ridges and lower levels over
smoother abyssal plains. Also, regions with strong deep flows, such as
the Samoan Passage through which bottom water is funneled into the North
Pacific, or the region south of the Campbell Plateau through which the
Antarctic Circumpolar Current flows, exhibit stronger deep internal wave
signatures.